1. Technical Field of the Invention
The present invention relates to novel liposoluble, photostable N-substituted benzimidazolyl-benzazole or benzofuryl-benzazole silicon-containing compounds which have excellent absorbing power in the UV radiation range.
This invention also relates to photoprotective compositions of matter, in particular, cosmetic sunscreen compositions containing the subject novel compounds which are useful for photoprotecting human skin and/or hair against UV radiation, in particular solar radiation.
2. Description of the Prior Art
It is known to this art that light radiation of wavelengths of from 280 nm to 400 nm promotes tanning of the human epidermis, and that irradiation of wavelengths, more particularly ranging from 280 to 320 nm, i.e., UV-B irradiation, causes skin burns and erythema which may be harmful to the development of a natural tan. For these reasons, as well as for aesthetic reasons, there is an increasing demand for means for controlling this natural tanning in order thus to control the color of the skin. This UV-B radiation should thus be screened from the skin.
It is also known to this art that UV-A radiation, of wavelengths of from 320 to 400 nm, which causes tanning of the skin, is also likely to adversely affect it, especially in the case of sensitive skin or of skin which is continually exposed to solar radiation. UV-A rays cause, in particular, a loss of elasticity of the skin and the appearance of wrinkles, promoting premature skin aging. Such irradiation promotes triggering of the erythemal reaction or amplifies this reaction in certain individuals and may even be the cause of phototoxic or photoallergic reactions. Thus, for aesthetic and cosmetic reasons such as conservation of the natural elasticity of the skin, for example, an ever-increasing number of individuals wish to control the effect of UV-A rays on their skin. It is thus desirable to also screen out UV-A radiation.
A wide variety of compounds intended for the photoprotection (against UV-A and/or UV-B) of the skin are known to this art.
Most are aromatic compounds which exhibit absorption of UV radiation in the region from 280 to 315 nm, or in the region from 315 to 400 nm, or in both of these regions. These are typically formulated into sunscreen/antisun compositions in the form of an emulsion of oil-in-water type (i.e., a cosmetically acceptable support comprising an aqueous dispersing continuous phase and an oily dispersed discontinuous phase) and which thus contain, in various concentrations, one or more conventional lipophilic and/or hydrophilic organic screening agents containing an aromatic function, which are capable of selectively absorbing the harmful UV radiation, these screening agents (and the amounts thereof) being selected as a function of the desired sun protection factor (the sun protection factor being expressed mathematically by the ratio of the irradiation time required to attain the erythema-forming threshold with the UV screening agent to the time required to attain the erythema-forming threshold without UV screening agent).
Other than their screening power, these compounds exhibiting anti-UV activity must also have good cosmetic properties in the compositions comprised thereof, good solubility in the usual solvents, and in particular fatty substances such as oils and fats, as well as good water-resistance and resistance to perspiration (remanence).
Among those aromatic compounds to date proposed for this purpose, exemplary are the N-substituted benzimidazolyl-benzazole compounds described in EP-A-0,843,995 or the benzofuryl-benzoxazole compounds described in EP-A-0,722,714. The solubility of these molecules in various formulations suited for photoprotection, however, still remains insufficient.